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Table 2 Pregnancies in Western Australia (2000–2013) and New South Wales (2002–2008) by plurality and Aboriginality

From: Pregnancy and birth characteristics of Aboriginal twins in two Australian states: a data linkage study

  Western Australia
(2000–2013)
New South Wales
(2002–2008)
Aboriginal Aboriginal Non-Aboriginal
Characteristic Twin
N = 880
n (%)
Singleton
N = 33,229
n (%)
Twin
N = 794
n (%)
Singleton
N = 31,524
n (%)
Twin
N 18,338
n (%)
Singleton
N = 582,355
n (%)
Groups compared and statistical significance reported1 A A B B C C
    D   D  
Gestation at first antenatal visitbCD, 2
 13 weeks or less 120 (49) 3797 (45) 508 (64) 18,955 (60) 13,894 (76) 410,156 (70)
 14 weeks or more n.p. 4551 (54) 270 (34) 11,545 (37) 4244 (23) 166,711 (29)
 No visit (WA) / No visit or missing (NSW) n.p. 125 (1) 16 (2) 1024 (3) 200 (1) 5488 (1)
Maternal health and pregnancy complications
 Gestational diabetesCd 48 (5) 1724 (5) 28 (4) 1105 e(4) 1095 (6)3 26,541 (5)
 Pre-existing diabetesbCd 8 (1) 557 (2) 12 (2) 230 (1) 142 (1) 3315 (1)
 Pre-eclampsia/eclampsia/gestational hypertensionABCd 148 (17) 2650 (8) 69 (9) 1618 (5) 2087 (11)3 31,855 (5)
 Pre-existing hypertensionC 18 (2) 415 (1) 8 (1) 286 (1) 237 (1)3 5547 (1)
 Threatened abortionA 56 (6) 1002 (3)
 Antepartum haemorrhageA 84 (10) 1787 (5)
 Threatened preterm labourA 256 (29) 3099 (9)
 Preterm prelabour rupture of membranesA 174 (20) 1695 (5)
  1. n.p. counts not publishable because of privacy concerns as they are either less than 5 or could lead to calculation of a count of less than 5. 1The superscripts ABCDabcd which appear next to the demographic factors indicate whether two groups were statistically significantly different: A or a for a comparison of WA Aboriginal singletons and twins; B or b for a comparison of NSW Aboriginal singletons and twins; C or c for a comparison of NSW non-Aboriginal singletons and twins; and D or d for a comparison of NSW Aboriginal twins and NSW non-Aboriginal twins. Pearson’s chi-squared tests were conducted. A capital letter indicates p < 0.001 and a lower-case letter indicates 0.001 < p < 0.05. 2WA and NSW have different definitions of gestational age at first antenatal visit. In WA, this information is reported by birth hospital and information on antenatal visits outside the hospital may be unavailable. Gestation at first antenatal visit was not recorded in WA until 2010 and data were missing for 25,410 infants in WA. This information was collected in NSW throughout the study period but from 2002 to 2005 mothers who did not receive any antenatal care could not be distinguished from mothers who did receive antenatal care, but their data was missing, so the two groups were combined in NSW. 3Some twin pairs had inconsistent information on their two birth records